1. Field of the Invention
The present invention relates to a spring plate to be used in a multiple disk friction coupling device such as a multiple disk clutch or a braking mechanism.
2. Description of Related Art
A dish-like spring plate 34 is installed in a prior art multiple disk clutch mechanism 30 shown in FIG. 19 which is one example of a multiple disk friction coupling device.
The spring plate 34 is pushed at the inner diameter end portion 42 by a piston 31, and in turn a mating plate 32 is pushed by an outer diameter end portion 43. The mating plate 32 thus pushed is pressed against a friction plate 33 which makes a mutual rotating motion, to thereby transmit a torque.
Since the spring plate 34 has an appropriate elasticity, a friction coupling pressure caused by the advance of the piston is made to rise gradually by this elasticity during the initial period of friction coupling, that is, to moderate sudden torque transmission.
The spring plate 34 is formed in a shape of dish as shown in FIGS. 20(a) and 20(b), having a uniform thickness in a radial direction. A face 39 to be pressed against, and facing, the piston 21 and the driving face 40 acting on the mating plate 32 are arranged mutually in parallel with each other and flat.
On the outer periphery of the spring plate 34 are formed teeth 36 which are engaged by means of splines with a drum 35.
The spring plate 34, when pressed by the piston 31, is sandwiched between the piston 31 and the mating plate 32, being elastically deformed from a dish-like shape to a nearly flat shape. Since the driven face 39 and driving face 40 of the spring plate 34 are mutually parallel and flat, the position of contact of the spring plate 34 with the piston 31 and the mating plate 32 hardly varies. That is, in FIG. 20(a), an inner diameter end portion 42 is in constant contact at the left corner with the piston 31, while an outer diameter end portion 43 is in constant contact at the right corner with the mating plate 32.
The spring plate 34 pressed by the piston 31 locally pushes with the right corner of the outer diameter end portion 43 the outer diameter end portion of the mating plate 32. Therefore, the mating plate 32 and friction material 37 of the friction plate 33 are mutually pressed firmer both at the outer diameter side than at other portions.
Therefore, greater frictional heat is generated at the both outer diameter sides of the mating plate 32 and the friction material 37, resulting in a high temperature of these members. In addition, since the frictional heat occurs locally on the outer diameter side and therefore can not easily escape, resulting in a locally higher temperature in this area.
Therefore, the spring plate 34 has such an inherent disadvantage that because of the parallelism and flatness of the driven face 39 and the driving face 40, each mating plate 32 is liable to heat distortion and also the friction material 37 to non-uniform seizure.
The corners of the inner diameter end portion 42 and outer diameter end portion 43 of the spring plate 34 are provided with chambers 44 and 45 as shown in FIG. 21; accordingly the contact position of the spring plate 34 relative to the piston 31 and the mating plate 32 varies little by little. However, because the chambers 44 and 45 are about 10% or less in the area of the driven face 39 and the driving face 40, the position subjected to a high temperature will hardly change.
Some spring plates have no tooth on the outer periphery as shown in FIGS. 22(a) and 22(b).
In the case of this spring plate 47 also, the driven face 46 and the driving face 49 are mutually parallel and flat, and the outer diameter end portion of the mating plate is locally pushed by the right corner of the outer diameter end portion 48; therefore the mating plate is liable to heat distortion and besides the friction material is easily subjected to ununiform seizure.
In the meantime the spring plate 54 installed in a multiple disk clutch mechanism 50 shown in FIG. 23 is pressed at an outer diameter end portion 55 by a piston 51 and in turn a mating plate (mating member) 52 is pressed by the inner diameter end portion 56.
In this spring plate 54 also both the inner diameter end portion of the mating plate 52 and the inner diameter end portion of friction material 57 of the friction plate (mating member) 53 reach a high temperature, easily causing heat distortion of the mating plate 52 and non-uniform seizure of the friction material 57.
The spring plates 34 and 54 and the mating plates 32 and 52 are engaged by means of splines with the drums 35 and 58 to thereby rotate together with the drums 35 and 58, and therefore will not mutually make a relative rotating motion. The spring plate 47 shown in FIG. 22 is provided with no tooth for spline engagement; however, since the piston and the mating plate rotate together as a unit with the drum, the spring plate 47 also will hardly make a relative rotating motion with the mating plate.
Consequently there will never occur any frictional heat between the spring plates 34, 47 and 54 and the mating plates.
Furthermore, the spring plates 34, 47 and 54 have such a problem also when assembled in an unillustrated multi-disk brake mechanism as the occurrence of non-uniform seizure and heat distortion of the mating member.